C 2 -Symmetric Bicyclic Bisborane Catalysts: Kinetic or Thermodynamic Products of a Reversible Hydroboration of Dienes

We prepared a new class of chiral C -symmetric bicyclic bisborane catalysts by addition reactions of internal dienes with the Piers borane, HB(C F ) , and an analogue, HB(p-C F H) . The dependence of the addition pattern on the reaction temperature allowed us to selectively prepare two diastereomeric catalysts from a single diene precursor. The bisboranes prepared in situ exhibited excellent activity (turnover numbers up to 200 at -40 °C) and enantioselectivity (up to 95 % ee) in imine hydrogenation reactions.